The former shadow environment secretary said on Friday that she suffered unwanted attention from her colleague over period spanning 20 years.
McCarthy said the Luton North MP sent her a series of letters and cards commenting on her appearance, including one in which he described having a dream about her.
Hopkins was suspended by the Labour Party earlier this week over allegations of sexual harassment.
McCarthy is the first MP to make specific claims of inappropriate behaviour since the Westminster scandal erupted.
McCarthy, who represents Bristol East constituency, told the Press Association she found his behaviour “upsetting” but did not feel she had anywhere to turn to about it.
She said she had been reassured and encouraged by the response she received after raising it with chief whip Nick Brown last Friday and party leader Jeremy Corbyn’s office on Monday.
But in a statement, Hopkins said McCarthy’s complaint had caused him “immense personal hurt and utter dismay” from someone he counted as a friend.
He added: “I cannot understand why a Parliamentarian of such experience and standing, who is also such a long term friend, would not have told me that she was unhappy with any aspect of our friendship rather than going straight to the national press.
“At a minimum I would have expected a Parliamentary colleague to raise any complaint through normal channels, allowing me due process and a fair chance to defend myself, if necessary.”
McCarthy said she believed Hopkins, who, she says, urged her in two of the notes to “dispose” of them, knew his actions were wrong.
“I never responded in any way, I never gave him any encouragement in any way, I tried to keep my distance as much as possible,” she said.
“I absolutely believe he knew this behaviour was unacceptable. It made me feel uncomfortable in his presence and was quite upsetting.”
She said she decided to go public after the “bravery” of a young activist, Ava Etemadzadeh, who complained last week about the behaviour of Hopkins.
He was suspended by Labour after Etemadzadeh contacted the party again with fresh information following an initial complaint over dealings with the MP in 2014 and 2015.
Hopkins was reprimanded at the time by then chief whip Dame Rosie Winterton but was appointed shadow culture secretary in 2016.
He “categorically denies” any inappropriate conduct in relation to Etemadzadeh.
McCarthy, 52, first met Hopkins, 76, when she was in her late 20s and they were both involved in Labour politics in her home town of Luton.
In 1994, when she was chairwoman of Luton North constituency Labour Party (CLP) and he chaired Luton South CLP, they went out for lunch, with McCarthy believing it was solely to discuss political issues.
He later sent her a card saying he had invited her “because you are attractive, intelligent and charming” before urging her to “dispose” of the note.
In a second note, Hopkins enclosed a photograph of McCarthy and described her as “pretty” before again asking her to dispose of it.
He also sent a postcard, which appears to be dated 1996, in an envelope to her place of work, asking whether her employer specialised in “pretty, petite brunettes”.
McCarthy said she went to another lunch with Hopkins because she found it awkward to say no to the invitation. He sent a card afterwards suggesting it “would be nice to meet again”.
On another occasion, also believed to be in 1996, McCarthy said Hopkins placed his hand on hers when she was not looking as she was getting out of a car.
A note sent in the run-up to the 1997 general election said: “You know I think you are lovely ... but I never see enough of you ... after May 1st perhaps ... K x”
The letters then reportedly stopped until her 50th birthday, when Hopkins sent a note on parliamentary writing paper to mark the occasion. By this time McCarthy was an MP.
A final letter was sent some time in 2015/16 but it is not clear if it was written after he was reprimanded for the incident involving Etemadzadeh.
In it, he described having a dream about McCarthy and said she remained a “very attractive woman”.
“I was upset by the unwanted attention. When it returned, I felt very angry,” she told the Press Association.
The Labour MP said it was important, as an older woman, to back up Etemadzadeh.
“You have a young woman who has been brave enough to speak out and is getting a hard time from some quarters about it,” she said.
“It is up to every woman to decide if they want to speak out or not. I chose not to in the past but I didn’t feel I could stay silent when my experience was so similar to hers.”
Although some of the complaints being made about sexual abuse and harassment in Westminster have been dismissed as low level by some commentators, McCarthy said the actions were part of a wider cultural problem which could deter young women from entering politics.
She added: “I have spoken to the chief whip and Jeremy Corbyn’s office about this but this was something they could not have been expected to know about until I brought it to their attention.”
Hopkins’ statement continued:
“If Kerry McCarthy MP raises a complaint with the Labour Party in the normal and fair way, I will of course fully cooperate with any investigation.
“However I do ask, on my behalf and on behalf of all other individuals and their families dealing with allegations, that these matters are dealt with by proper due process and not by unfair, humiliating one-sided trial by media.
“I am a 76-year old man and the stress this has caused me and my family is unbearable.
“All I ask for is proper due process and not to be convicted and vilified by the press before the details of the allegations are even investigated and put to me properly if they need to be.”